The present invention relates to refrigeration systems in general, and more particularly to refrigeration systems which provide cooling for air as well as machinery fluids.
Many industrial processes require control of the temperature of the material being processed and often of the machines handling the material. Particularly in the food industry an entire plant may be cooled to prevent spoilage and the growth of bacteria in foodstuffs. This is particularly a concern with meat, where it is important to control bacterial growth to assure product safety.
In an industrial setting, ammonia is often employed as a refrigerant. Ammonia is low cost and an efficient refrigerant for the temperature range of interest in many industrial processes. The hazards associated with ammonia: flammability and toxicity if inhaled, are safely handled in an industrial setting where safety practices and monitoring equipment can be reliably employed. Thus, for industrial processes, ammonia is one of the most widely used refrigerants.
Ethylene glycol is a widely used coolant. When used alone or mixed with water it has excellent heat absorbing characteristics, good thermal conductivity, and remains liquid over a broad temperature band. Whereas ammonia is used in a refrigerator or heat pump to transport heat energy from a cool reservoir to a warm reservoir, ethylene glycol transports heat from a warm reservoir to a cool reservoir.
In industrial plants, merely keeping the air at a desired temperature will not typically ensure that a material being handled within the plant remains near the air temperature. Machines which perform work convert energy stored as hydraulic pressure into mechanical motion. Most of the energy, however, is eventually converted into heat. Where a material is worked by a machine, the machine and the material may become undesirably heated. For machines employing hydraulic fluid to transfer energy, a typical process is to cool the hydraulic oil used by individual machines by passing water through a heat exchanger so that heat from the oil is given up to the cooling water.
Ground water is sometimes used as a low cost source of cooling fluid to extract heat from hydraulic oil. Water has a high specific heat and when pumped from below the ground typically has a temperature, determined principally by latitude, which in the Midwest is typically in the neighborhood of 55 degrees Fahrenheit. In the past this ground water could be obtained at the cost of pumping it from the ground.
Modern industrial plants, particularly those handling organic material, are typically connected to their own or to a municipal sewage treatment plant. Particularly when connected to a municipal sewage treatment plant, the cost of treatment is based on the amount of water consumed. Thus the use of an open loop water cooling system can have considerable negative economic consequences.
What is needed is an efficient method and apparatus for closed loop cooling of machine hydraulic fluids.